1. Field of the Invention
The invention relates to a device for the transport of multilayer, edge-perforated imprint-receiving substrates, which are movable along a curved transport path, with a thrust tractor pair disposed in front of a substrate support in transport direction, as well as with at least one friction roller pair with respectively at least one driven friction roller, where a pulling force can be transferred by way of the driven friction roller, and wherein the multilayer imprint-receiving substrate rests with its rear layer on the substrate support.
2. Brief Description of the Background of the Invention Including Prior Art
Such devices can be distinguished from other conventional devices, where only a single-layer sheet paper is processed by the necessary structural changes for balancing the generally unequal pull exerted onto the front or the rear layers of the multilayer imprint-receiving substrate.
Different radii of the front and rear layer and thus a differently extended paper length result during the transport of multilayer paper through a curve-shaped channel. A pulling force is exerted onto the multilayer form paper during operation with a thrust tractor along the straight path of the transport. In case of a deficient connection of the form packages relative to each other, there can occur various malfunctions of the equipment including jamming and erroneous and defective operations. The pulling force on the front layer is so large that this layer migrates upwardly at the pin of the tractor gear belt and possibly tears the paper. The imprint-receiving substrate then skips and slides out of the thrust tractor. In the other case, where the pulling force onto a rear layer is too low, there is formed a bulge ahead of a friction roller pair disposed following the thrust tractor, i.e. the paper becomes curved and causes a paper jamming during the further course of the transport motion.
It is known to transport single-layer paper over a curved transport path as taught, for example, in the German Patent document DE 3,607,080. The known structure is suitable for individual sheets and for continuous paper bands. It is however of major importance in this connection that already advanced imprint-receiving substrates are also withdrawn again from a joint feed channel, in order to hold one or the other imprint-receiving substrate in waiting position. In this regard, however, the thrust tractor is nevertheless of importance in this context in that the thrust tractor feeds and advances the imprint-receiving substrate resting tightly on a press-on bar. As long as the tip of the imprint-receiving substrate lies only on the press-on bar, no pulling force is generated within the imprint-receiving substrate. Such a device consequently does not readily take into consideration a multilayer imprint-receiving substrate.
For example, multilayer imprint-receiving substrates comprise a thicker "front" original sheet and one or several thinner "rear" sheets made of so-called copy paper. According to this definition, the thicker front original sheet is disposed at the bottom side of the thrust tractor, whereas the thinner copy paper is disposed at the upper side of the thrust tractor, i.e. immediately under the conventional flip cover for the thrust tractor.